The present invention relates to an organic substance processing system and an organic substance processing apparatus for heating fluid containing organic substances and oxidizing them, or changing then to oil or low molecular weight compounds, and especially relates to an organic substance processing system and an organic substance processing apparatus which continuously processes fluid containing organic substances.
A technique has recently been developed to oxidize sludge in sewage containing a lot of organic substances or drainage from factories, which also contains organic substances, by pressurizing and heating it to a pressure value and a temperature value beyond the critical levels (in the case of water, the pressure=22 Mpa, and the temperature=374.degree. C.). A technique has also been developed to change sludge to oil below the critical conditions but under high pressure and high temperature conditions. Further, for recycling abandoned plastics, another technique is also known to decompose plastics with high molecular weight compounds in supercritical fluid and recover them as raw materials with low molecular weight compounds.
In every one of the above system, the processing of organic substances is performed by pressurizing fluid containing the organic substances to a high pressure level and heating it. A high-pressure slurry pump is generally used to pressurize fluid containing organic substances to a high pressure. However, a high-pressure slurry pump is a specialized pump and very expensive. Japanese Patent Application Laid-open Hei 5-111695 discloses a sludge pressing-in apparatus with a high-pressure water pump as a pressurizing apparatus in place of a slurry pump.
A method of reducing the power necessary to feed slurry at a high pressure is disclosed in "The Development of Continuous Pipeline System Autoclave" by Nakamich Yamasaki et al., A report of The Research Laboratory of Hydrothermal Chemistry, Faculty of Science Kochi University, Vol. 3, pp 1-4 (1979), which is referred to as a known literature.
Since processed fluid is pressurized to a high pressure level to oxidize organic substances in supercritical water, changes sludge to oil, or make plastics into low molecular weight compounds, a very large amount of power is necessary for the pump. In the method disclosed in the known literature, by using the pressure of the fluid in the reaction system for the back-pressure of the reaction system, the power driving the pump is reduced. However, according to this method, it is necessary to take new fluid to be processed into a cylinder, after the cylinder has been emptied by expelling the fluid to be processed in the reaction system from the cylinder. Therefore, fluid to be processed in the reaction system cannot be continuously fed from the cylinder to a reactor. Moreover, since a pressure regulation valve is located downstream from the cylinder, a great deal of auxiliary power is required to feed fluid into the cylinder while suppressing changes of pressure in the reaction system.
Further, as disclosed in Japanese Patent Application Laid-Open Nei 5-111695, when oxidization processing is performed in supercritical water, it is necessary to mix high-pressure oxygen gas into high-pressure fluid containing organic substances. If the flow rate of the fluid containing organic substances varies in this mixing process, the ratio of the oxygen gas to the fluid containing organic substances also changes. Accordingly, oxidization processing of organic substances does not uniformly occur. Furthermore, if the feed flow rate of the fluid containing organic substances changes, the residence time of the fluid in a preheater or a reactor varies, and the processing other than the oxidization processing also does not uniformly proceed. Thus, when fluid containing organic substances is fed at a high pressure, changes in the feed flow rate of the fluid must be suppressed as much as possible. The most effective method of suppressing changes of the feed flow rate of the fluid is to use a pump of a large capacity, which requires a very large amount of power for the pump.